This invention relates to a process for preparing L-fructose alone or in admixture with polyols, such as L-mannitol and L-sorbitol.
L-sugars are useful as sweetening agents because, as disclosed in U.S. Pat. No. 4,262,032, they are sweet like the D-sugars, but unlike D-sugars, L-sugars are either not metabolized by the body or are metabolized to a lesser extent than the D-sugars. These features make L-sugars desirable as sweeteners for individuals wishing to reduce caloric-intake or for individuals unable to metabolize common sugar sweetening agents without detrimental effects, e.g., diabetics. Another advantage associated with L-sugars is the absence of an objectionable aftertaste commonly experienced with artificial sweeteners such as saccharin and the cyclamates. However, as desirable as the L-sugars are in the foregoing respects, their relative scarcity in nature, particularly L-glucose and L-fructose, the laevo counterparts of the two monosaccharide sweeteners most commonly used today, has prevented their widespread use in foods and beverages or even their being considered for use in such products.
D. Shaw, "Polyol Dehydrogenases", Biochem. J., 64 (1956), pp. 394-405, the contents of which are incorporated by reference herein, describes the oxidation of D-gulitol, a polyol identical to L-glucitol and L-sorbitol, by employing D-iditol dehydrogenase isolated from a species of Pseudomonas cultivated in a nutrient medium containing dulcitol which is required to induce the microorganism to produce the enzyme. The need for dulcitol, which must be extracted from certain plants or obtained by hydrogenation of lactose, imposes a considerable limitation on the practical usefulness of the Shaw process.